The presented circuit uses an opto-SCR. We found the circuit in the GE semiconductor manual. Equivalent triacs, depending on the load current and voltage, can be used.
We found this circuit in a Radio Electronics from October 1960. The circuit uses just one...
Using components from the era, this 90's EDN circuit is used in analog to digital conversion...
Found in National Semiconductor documentation from the 1980s, this oscillator is used for...